A conventional silicon carbide (SiC) Schottky diode comprises an n-type SiC substrate, on which an n− doped drift layer is epitaxially grown. This drift layer is contacted by a Schottky contact. Surrounding the Schottky contact a p doped junction termination extension (JTE) layer may be arranged in order to lower the electric field peak on the edge of the Schottky contact and to smoothly lower the electric field towards the edge of the diode. Additionally to the JTE layer, concentric floating p doped guard rings may be around the JTE layer to avoid high field peaks on the surface of the Schottky diode in the termination region.
In WO 2009/108268 A1 a prior art silicon carbide Schottky diode is described, which has an edge termination structure with a plurality of spaced apart concentric floating guard rings, which are p doped. Each of the guard rings comprises a highly doped portion and a lightly doped portion. Such a diode needs multiple ion implantation for the forming of the higher and lower doped portions. Different masks have to be applied and typically, different ions are used to create the different doping concentrations and preferably also different diffusion depths. This makes the manufacturing costly. At the same time, it increases demands on the alignment precision and reproducibility of lithographical processing steps and/or it reduces production yield. Due to the misalignment of highly and lightly doped p-regions in production, the enhancement of the blocking voltage might not be as high as predicted by the device simulation.
“Radiation Produced in 4H—SiC Epilayers by Alpha-Particle Irradiation”, Materials Science Forum, vol. 740-742, 2013, 661-664, concerns a prior art method for the creation of a lower doped layer in an n-doped 4H—SiC epi layer for a diode created by a single irradiation with 550 keV protons.
US 2014/374774 A1 describes a method for creating an (n−−) lowly doped layer between an (n−) doped drift layer and an (n+) doped layer. All layers are created by epitaxial growth. The doping reduction layer overlaps with p doped termination layers in form of p guard rings, i.e. the doping reduction layer is shallower than the guard rings.